Use evil trickery to become hard to find (7)
I believe the answer is:
elusive
'hard to find' is the definition.
(something elusive is hard to find)
'use evil trickery' is the wordplay.
'trickery' indicates anagramming the letters.
'use'+'evil'='useevil'
'useevil' with letters rearranged gives 'ELUSIVE'.
'to become' is the link.
(Other definitions for elusive that I've seen before include "Hard to find" , "Difficult to catch or see" , "Hard to get hold of" , "Use veil to be difficult to catch" , "Difficult to find or catch" .)